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.\" Author: Alexey Ishchuk <aishchuk@linux.vnet.ibm.com>
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.TH S390_PCI_MMIO_WRITE 2 2021-03-22 "Linux Programmer's Manual"
.SH NAME
s390_pci_mmio_write, s390_pci_mmio_read \- transfer data to/from PCI
MMIO memory page
.SH SYNOPSIS
.nf
.B #include <asm/unistd.h>
.PP
.BI "int s390_pci_mmio_write(unsigned long " mmio_addr ,
.BI "                       const void *" user_buffer ", size_t " length );
.BI "int s390_pci_mmio_read(unsigned long " mmio_addr ,
.BI "                       void *" user_buffer ", size_t " length );
.fi
.PP
.IR Note :
There are no glibc wrappers for these system calls; see NOTES.
.SH DESCRIPTION
The
.BR s390_pci_mmio_write ()
system call writes
.IR length
bytes of data from the user-space buffer
.IR user_buffer
to the PCI MMIO memory location specified by
.IR mmio_addr .
The
.BR s390_pci_mmio_read ()
system call reads
.I length
bytes of
data from the PCI MMIO memory location specified by
.IR mmio_addr
to the user-space buffer
.IR user_buffer .
.PP
These system calls must be used instead of the simple assignment
or data-transfer operations that are used to access the PCI MMIO
memory areas mapped to user space on the Linux System z platform.
The address specified by
.IR mmio_addr
must belong to a PCI MMIO memory page mapping in the caller's address space,
and the data being written or read must not cross a page boundary.
The
.IR length
value cannot be greater than the system page size.
.SH RETURN VALUE
On success,
.BR s390_pci_mmio_write ()
and
.BR s390_pci_mmio_read ()
return 0.
On failure, \-1 is returned and
.IR errno
is set to indicate the error.
.SH ERRORS
.TP
.B EFAULT
The address in
.I mmio_addr
is invalid.
.TP
.B EFAULT
.IR user_buffer
does not point to a valid location in the caller's address space.
.TP
.B EINVAL
Invalid
.I length
argument.
.TP
.B ENODEV
PCI support is not enabled.
.TP
.B ENOMEM
Insufficient memory.
.SH VERSIONS
These system calls are available since Linux 3.19.
.SH CONFORMING TO
This Linux-specific system call is available only on the s390 architecture.
The required PCI support is available beginning with System z EC12.
.SH NOTES
Glibc does not provide wrappers for these system calls; call them using
.BR syscall (2)
.SH SEE ALSO
.BR syscall (2)
